#define _CRT_SECURE_NO_WARNINGS 1
#include<stdio.h>
#include<assert.h>
char* my_strcat(char* des, char const * src) {
	char* ret = des;
	assert(des && src);
	while (*des)des++;
	while (*des++ = *src++);
	return ret;
}
int main() {
	char a[100] = "123";
	printf("%s", my_strcat(a, "45678910"));
	return 0;
}